Presently, as for members, which are required to exhibit wear resistance, sliding properties, and fracture resistance, such as cutting tools, wear-resistant members, and sliding members, wear resistance, sliding properties, and fracture resistance are enhanced by using a technique of forming a coating layer on surfaces of a substrate composed of a sintered alloy such as a cemented carbide, cermet, or the like, a high-hardness sintered body such as diamond or cBN (cubic boron nitride), or a ceramic such as alumina, silicon nitride, or the like.
Extensive studies have been conducted on methods for forming coating layers in which a physical vapor deposition process such as an arc ion plating process or a sputtering process is used to form nitride layers containing Ti or Al as a main component, and continuous improvements have been made to extend tool life. Various innovations other than elements used in the coating materials have been applied to these surface-coated tools having coating layers in order to comply with changes in cutting environment such as increasing cutting speeds and diversification of workpieces.
For example, PTL 1 describes a surface-coated tool in which surfaces of a substrate are coated with a coating film such as TiAlN and that progress of welding and wear at a rake face can be suppressed and notch wear at a flank face can be suppressed by making the Ti ratio in the flank face higher than the that in the rake face.
PTL 2 describes formation of a TiAlN-based hard coating film having a thickness of 1 to 5 μm on surfaces of a substrate, and describes that the hard coating film exhibits improved welding resistance and wear resistance by making coarse particles, which are larger than the thickness of the coating film and are present in the hard coating film, 5 area % or less, and by making the surface roughness Ra thereof 0.1 μm or less or the surface roughness Rz 1 μm or less.
PTL 3 discloses formation of a film having a composition such as (TiNbAl)N on surfaces of a substrate to improve wear resistance, and PTL 4 describes a hard-coating film having a composition such as (TiAlNbSi)N in which multiple layers having different contents of Si and Nb are stacked by changing coating processes.
PTL 5 discloses a (Ti,Al,W,Si,M)N coating layer (where M represents at least one element selected from the group consisting of Nb, Mo, Ta, Hf and Y) which exhibits a good oxidation resistance and a good wear resistance.